The present invention relates to catalysts, and more particularly, to a method of fabricating catalysts on a nanometer scale for wide ranging industrial applicability. The invention also relates to the catalyst structures so formed.
Because of its economic importance, catalysis is one of the most intensely pursued subjects in applied chemistry and chemical engineering. Catalysts are widely used today to lower the activation energies that would otherwise prohibit important reactions from proceeding. Most industrial reactions are catalytic, and many process improvements thereto result from the discovery of better chemical routes, or as the result of attaining new ways to position catalysts to better interact with important chemical reactants. Ideally it is often best to expose as much of the catalyst as possible to the reactants in the reaction scheme.
Unfortunately, to-date, catalysis has been an inexact science on other than a macroscopic scale. Scientists are only beginning to understand the microscopic interplay between the catalyst and the surface or substrate upon which it is positioned. :It is believed that these surface interactions may have a significant impact on ultimate catalyst stereochemistry and performance.
However, because of current process technological limitations it has been difficult to provide reaction vehicles which would facilitate microscopic catalyst formation. What is therefore needed in the art is a new method of forming a catalyst body that takes maximum advantage of the chemical and physical properties of both the catalyst and the substrate upon which it is formed at a nanometer-scale level.
The invention provides a method of forming a catalyst body on a nanometric scale sufficient to carry out microscopic (nanometric) catalysis reactions. The method comprises forming a first layer of hemispherical grain polysilicon over a substrate. At least a portion of the first layer is then oxidized to form a second layer of silica over the remaining portion of the first layer which has not been oxidized. A third layer of nitride is formed over the second layer, and a catalyst material is deposited on the nitride layer. The catalyst material is then annealed to form a catalyst body which causes the catalyst material to have a larger exposed surface area than just prior to annealing.
The invention provides a method for increasing the surface area of a catalyst material. A barrier layer is formed over a layer of silica, and a layer of catalyst material is then deposited over the barrier layer so as to form a catalyst body. The catalyst material incorporated into the catalyst body has more exposed surface area for reaction than when it has not been made a part of the catalyst body.
The invention also provides a method of converting a portion of hemispherical grain polysilicon to silica without substantially flattening the textured grain itself. The grain is heated to a temperature within the range of about 350 to about 750 degrees C for a period not exceeding about 5 minutes.
The invention provides a catalyst body which has a first layer of hemispherical grain polysilicon, a second layer of silica formed from a portion of the polysilicon, a third layer of silicon nitride provided over the second layer, and a catalyst material layer provided over the third layer. The catalyst material layer is made up of at least one member selected from Group VIII metals and zeolites.
The invention provides a catalyst body having a first layer of hemispherical grain polysilicon, a second layer of silica formed from a portion of the hemispherical grain polysilicon, and a catalyst material layer formed over the second layer.
The invention also provides a sensor device which has a catalyst body formed over a substrate. The catalyst body comprises a first layer of hemispherical grain polysilicon, a second layer of silica formed over the first layer, a third layer of nitride formed over the silica layer, and a catalyst material layer formed over the nitride layer. It is desirable that the catalyst material layer be more expansive, e.g. extend further perimeter wise, than at least one of the underlying layers.
These and other advantages and features of the present invention will become more readily apparent from the following detailed description and drawings which illustrate various exemplary embodiments.